Elongation sensors of that type are known in the art in a variety of configurations and reference may be had, in that connection to German patent document DE 102 01 880 A1 and US patent application publication US 2005/0017710 A1.
Such a magnetostrictive elongation sensor has as a rule a wire-like or tubular waveguide extending in a measurement direction and provided from a magnetostrictive material. By means of a position magnet which is displaceable relative to the waveguide and along the waveguide, the contactless application of a magnetic field to the waveguide can result in a mechanical elastic wave therein. That mechanical elastic wave spreads in both directions along the waveguide and can be detected by the signal processing circuit as an end of the waveguide. From the propagation time of the wave along the waveguide, the exact spacing of the position magnet from the end of the waveguide can be determined and thus the position of the movable component, element or point to which the position magnet is affixed.
The waveguide is usually received in a support body, for example a tube, in order to provide a mechanically stable mounting of the sensing element and to permit it to be affixed to a component with respect to which the movable point is displaceable. The electronic parts forming the signal processor, for example, are usually arranged at one end of the waveguide. These can include a detector coil, a Villary-effect strip, the signal processing circuitry and optionally a diagnostic output. All of these elements can be provided in a housing and thereby protected against environmental effects.
On a machine to be monitored, it is not uncommon to provide a number of such elongation or longitudinal displacement sensors. At standstill of the machine it is important to be able to identify possibly defective parts of the apparatus as quickly as possible to thereby keep production losses to a minimum. Since both maintenance and restoring the apparatus to full production can result in operational interruptions or lags, it is essential to be able to diagnose a possible failure of the sensor as quickly as possible.
There are in the art sensors having BUS type interfaces which have been described as having optical diagnostic outputs. However, these optical diagnostic outputs themselves are exclusively provided by the BUS communication.